804. There are on the market several anastigmatlenses working at a great relative aperture. Theoretically, their speed leaves nothing to be desired; but when they are used at full aperture the extent of the field sharply covered is not sufficient to allow one to make practical use of their speed.

805.. To overcome this difficulty the focal length of these lenses is generally increased, which accentuates all the more the lack of "depth of focus," already very noticeable because of their large relative aperture. Consequently, a fast lens to be really serviceable for general photographic work, should not only possess speed, but should at the same time cut sharply, at full aperture, an image contained within an angle of 60 degrees, or, in other words, a plate the longer side of which is about equal to the focal length of the lens.

806. The Celor Lens combines these properties. It has its place, therefore, in all up-to-date studios.

807. We claim that Celor lenses are superior to all other anastigmats of equal maximum aperture, because of their larger field of sharp definition at full aperture. This enables one to select a Celor lens of shorter focal length than that of other similar anastigmats, an important consideration where the length of the studio is limited. This is a great advantage for the photographer, meaning, as it does, a gain in the depth of focus, and incidentally in actual working speed.

808. The back combination of the Celor can be used as a single lens of double the focal length. At F. 32 it will yield about the same definition as the whole lens and twice the covering power of the latter.

809. Goerz Dagor

810. Although it is but a few years since public attention was first attracted to the Goerz Double Anastigmat Dagor (Series III.), these lenses have won the most extended recognition, not only from authorities in photographic optics who have been in position to exhaustively test their merits, but from the photographic confraternity at large, whether amateur or professional. (See Illustrations Nos. 70 and 71).

811. The Dagor lens is a universal instrument in the full sense of the word, and comes as near being an all around lens as can be hoped for, considering the manifold and complex requirements of the photographic craftsman.

812. Each Goerz Double Anastigmat Dagor supplies 1st. A rapid lens for general purposes - portraiture, landscape, architecture, enlargements, etc., working at full aperture with extreme sharpness to the edges of the plate for which it is constructed. 2d. A wide angle lens for interiors and all views at shortdistances, sharply covering a much larger plate when smaller apertures are employed. 3d. A long focus lens for distant objects, when the back combination alone is used.